A modified design approach for compact ultra‐wideband microstrip filters

A modified design approach for compact ultra‐wideband microstrip filters with cascaded/folded stepped‐impedance resonators is described. The key feature of the proposed method is to facilitate stronger coupling between stepped‐impedance resonators and, at the same time, eliminate the requirement of extremely small gaps in coupled‐line sections, as found in traditional designs. Simulations and measurements demonstrate that the filters designed with this technique exhibit good reflection, insertion‐loss, and group‐delay performance within the 3.1–10.6 GHz band. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE 2010.     

Singular value decomposition improves accuracy and reliability of T-septum waveguide field-matching analysis

A singular value decomposition (SVD) is used to solve the characteristic matrix equation of 2 different field-matching analyses as applied to T-septum waveguide structures. It is demonstrated that SVD avoids the need for complicated numerical zero-detection algorithms, eliminates the major disadvantages of the classical field-matching technique, and hence, improves the accuracy and reliability of the computed results. The values obtained are in close agreement with available theoretical data and measurements.     

Dielectric slab matched ferrite gyrator

A 180° nonreciprocal ferrite phase shifter with stepped dielectric impedance transformer sections at both ends is designed using the method of field expansion into eigenmodes. The rigorous optimisation method includes the higher-order mode interaction between the step discontinuities. The design achieves compact and simple components, as relatively thick, and consequently short, uniform ferrite slabs of standard dimensions may utilised. A computer-optimized design example provides about 180° ± 1° nonreciprocal differential phase shift between 12.2 and 12.8 GHz together with more than 24dB return loss.     

VUV generation by high-order CARS

Generation of VUV (vacuum ultraviolet) radiation by stimulated Raman scattering (SRS) in H₂ is studied with collinear irradiation of the first Stokes component simultaneously with pump laser radiation. Improvements of the high-order coherent anti-Stokes Raman scattering (CARS) method over the pure SRS scheme are: generation of higher anti-Stokes (AS) orders, increased conversion efficiency, and considerably better reproducibility. Experimental results are presented to confirm the theoretical analysis     

Inline TM/sub 110/-mode filters with high-design flexibility by utilizing bypass couplings of nonresonating TE/sub 10/01/ modes

This paper presents a new class of pseudoelliptic function filters that are based on compact inline TM/sub 110/-mode cavity configurations. No structural folding is required. The bypass couplings are implemented through the nonresonating TE/sub 10/01/ modes so that arbitrarily positioned transmission zeros can be implemented. Design guidelines to generate a given transmission zero on the desired side of the passband and how to control it are presented. To demonstrate its flexibility, the approach is illustrated at examples of four-pole inline filters providing Chebyshev, elliptic-function-type, and asymmetric characteristics. Performance comparisons with different numerical codes validate the designs. A fourth-order pseudoelliptic filter with four transmission zeros is then designed, constructed, and measured. Excellent agreement between simulated and experimental results verifies the approach.     

Computer-aided design of multilayered dielectricfrequency-selective surfaces for circularly polarized millimeter-waveapplications

A procedure for the computer-aided design of dielectric-layered frequency-selective surfaces is introduced. Emphasis is placed on millimeter-wave applications involving circularly polarized incident signals. The design routine incorporates filter theory for high-low impedance structures and analysis concepts known from thin-film optics which include the losses of the materials. For given material constants and performance specifications, the exact thicknesses of the dielectric layers as well as the angle of the incident wave are determined by applying optimization strategies. A 40-GHz design example demonstrates the attractiveness of the design in circularly polarized millimeter-wave frequency-selective surface applications     

Adaptive multivlevel methods in three space dimensions

We consider the approximate solution of self-adjoint elliptic problems in three space dimensions by piecewise linear finite elements with respect to a highly non-uniform tetrahedral mesh which is generated adaptively. The arising linear systems are solved iteratively by the conjugate gradient method provided with a multilevel preconditioner. Here, the accuracy of the iterative solution is coupled with the discretization error. As the performance of hierarchical bases preconditioners deteriorates in three space dimensions, the BPX preconditioner is used, taking special care of an efficient implementation. Reliable a posteriori estimates for the discretization error are derived from a local comparison with the approximation resulting from piecewise quadratic elements. To illustrate the theoretical results, we consider a familiar model problem involving reentrant corners and a real-life problem arising from hyperthermia, a recent clinical method for cancer therapy.     

Visual Analysis of Confocal Raman Spectroscopy Data using Cascaded Transfer Function Design

2D Confocal Raman Microscopy (CRM) data consist of high dimensional per‐pixel spectral data of 1000 bands and allows for complex spectral and spatial‐spectral analysis tasks, i.e., in material discrimination, material thickness, and spatial material distributions. Currently, simple integral methods are commonly applied as visual analysis solutions to CRM data which exhibit restricted discrimination power in various regards. In this paper we present a novel approach for the visual analysis of 2D multispectral CRM data using multi‐variate visualization techniques. Due to the large amount of data and the demand of an explorative approach without a‐priori restriction, our system allows for arbitrary interactive (de)selection of varaibles w/o limitation and an unrestricted online definition/construction of new, combined properties. Our approach integrates CRM specific quantitative measures and handles material‐related features for mixed materials in a quantitative manner. Technically, we realize the online definition/construction of new, combined properties as semi‐automatic, cascaded, 1D and 2D multidimensional transfer functions (MD‐TFs). By interactively incorporating new (raw or derived) properties, the dimensionality of the MD‐TF space grows during the exploration procedure and is virtually unlimited. The final visualization is achieved by an enhanced color mixing step which improves saturation and contrast.